Le but de cette étude est de retracer l’évolution de l’hydrologie dans la partie occidentale de l’Océan Pacifique subtropical en utilisant le proxy εNd analysé sur les foraminifères et sur les oxydes de ferromanganèse authigéniques dans les sédiments. Ceux-ci proviennent de carottes sédimentaires prélevées au nord de la Mer de Chine du Sud (MCS). Avant d’utiliser l’εNd dans les sédiments profonds de la MCS, 16 profils d’eau de mer, collectés au nord de la MCS et dans le Mer des Philippines, ont été analysés afin d’établir la distribution d’εNd des masses d’eau dans l’ouest du Pacifique tropical et dans la MCS, qui jusqu’à aujourd’hui n’était pas documentée. Les valeurs d’εNd des masses d’eau profondes et intermédiaires varient de -2,7 à -4,4 et augmentent légèrement avec la profondeur. Dans la mer des Philippines, les valeurs d’εNd de l’eau intermédiaire du Pacifique Nord (North Pacific Intermediate Water, NPIW) atteint -2.7±0.4 à moyenne profondeur (500 à 1400m). En-dessous de de 1800m, l’eau profonde Pacifique (Pacific Deep Water, PDW) est caractérisée par du Nd moins radiogénique (-4.1±0.5), indiquant l’intrusion de masses d’eau australes. Pour la plupart des stations du nord de la MCS, les masses d’eau en-dessous de 1500m (PDW) affichent des valeurs d’εNd homogènes (~ -4.1), similaires à celles de la PDW dans la Mer des Philippines. Les valeurs d'εNd pour l'eau intermédiaire de la mer de Chine du Sud (South China Sea Intermediate Water, SCSIW, 500-1500m) varient entre -3.0 et -3.9 dû au mélange vertical de la NPIW avec la PDW. Les valeurs d'εNd de l'eau de mer dans la MCS (-5.3 à -7.0) affichent des modifications locales dans des zones où l'eau s'écoule au-dessus de systèmes de dépôt sédimentaire. Ceci implique que "l'échange à la marge" avec des sédiments non radiogéniques (autour de -11) peut se produire dans le temps et dans l'espace sans modifier la composition isotopique du Nd de la PDW dans le Nord de la MCS. Dans un second temps, l’εNd extrait des foraminifères planctoniques G. ruber a été étudié sur la carotte MD05-2904, collectée à 2000m de profondeur sur la marge nord-ouest de la MCS. Cette étude a été conduite dans le but de retracer les variations hydrologiques depuis le Dernier Maximum Glaciaire (DMG) dans la partie occidentale du Pacifique Nord subtropical. Les enregistrements d'εNd ainsi obtenus couvrent les derniers 25 000 ans. Ils affichent une large gamme de valeurs de -4±0.2 à -6.7±0.3, suggérant d'importants changements dans la contribution de la NPDW (εNd=-4) et de la UCDW (Upper circumpolar Deep Water, εNd -6 to -8) dans la zone étudiée. Durant la déglaciation, les enregistrements d'εNd indiquent une diminution des excursions négatives de l'εNd impliquant une plus forte proportion de SSW (Southern-sourced Water) entre 17 et 15 ka BP ainsi qu'entre 10 et 8 ka BP. Ces intervalles de temps sont contemporains de l’évènement Heinrich 1 (HS1) et de l’Holocène inférieur. Les shifts négatifs centrés sur le HS1 coïncident avec un phénomène d'upwelling renforcé dans l'océan austral, associé à un déplacement vers le pôle des vents d'ouest. Ceci implique une augmentation de la formation de la SSW qui se propage dans l'Ouest du Pacifique subtropical. L'excursion négative de l'εNd durant l’Holocène inferieur (~10-8 cal ka BP) indique une plus grande proportion de SSW qui pourrait être associée avec une plus forte production de SSW, comme observé récemment dans l'atlantique Sud, et/ou avec une possible réduction de la NPIW. Nos données suggèrent que le schéma de circulation actuel dans la partie occidental du Pacifique subtropical s'est mis en place il y a 4600 ans. / The aim of this study is to reconstruct the evolution of the hydrology of the western subtropical North Pacific Ocean by using εNd proxy analysed on foraminifera and dispersed authigenic ferromanganese oxide precipitates in sediments from deep-sea cores collected in the northern SCS. Before using the εNd proxy on deep sea sediments of the SCS, Nd of 16 seawater profiles collected in the northern South China Sea (SCS) and the Philippine Sea were investigated to establish the εNd distribution of water masses along the tropical western Pacific and the SCS that, until now have not been documented. εNd values for mid- and deep-water masses of the Philippine Sea and the SCS range from -2.7 to -4.4 and generally increase slightly with water depth. In the Philippine Sea, εNd values for the North Pacific Intermediate Water (NPIW) reach- 2.7±0.4 at mid-depths (500 to 1400 m). Below ~1800 m, the Pacific Deep Water (PDW) is characterized by less radiogenic Nd (-4.1±0.5) indicating the instrusion of southern sourced water masses. For most of the stations in the Northern SCS, water masses below 1500m (PDW) display homogenous εNd values (~ -4.1) similar to those of the PDW in the Philippine Sea. εNd values for the South China Sea Intermediate Water (SCSIW, 500-1500m) vary from -3.0 to -3.9 as a result of the vertical mixing of the NPIW with the PDW in the SCS. Seawater εNd values for the SCS (~5.3 to -7.0) display local modification in areas where the water lies above sediment drift deposit systems. This implies that “boundary exchange” with unradiogenic sediments (around~11) may occur temporally and spatially and does not modify he Nd isotopic composition of the PDW in the Northern SCS. In a second step, seawater εNd extracted from cleaned planktonic foraminifera G. ruber has been investigated on core MD05-2904, collected at a deph of 2000m on the north-western margin of the SCS. This study was undertaken in order to reconstruct hydrological variations since the LGM in the western subtropical North Pacific. The εNd records obtained from foraminifera spanning the past 25kyr. Display a wide range of values, ranging from -4±0.2 to -6.7±0.3, suggesting important changes in the contribution of the NPDW (εNd=-4) and the UCDW (εNd -6 to -8) in the subtropical western Pacific. During the period of deglaciation, εNd records indicate a relative decrease in the negative excursions of the εNd implying a higher proportion of SSW during the time intervals 17-15 cal kyr BP and 10-8 cal kyr BP; these intervals are coeval with the HS1 and early Holocene. The negative shifts centered on the HS1coincide with an enhanced upwelling in the Southern Ocean, associated with a polewards shift of the southern westerlies, inducing an enhanced formation of the SSW that propagates to the subtropical western Pacific. The negative excursion of the εNd during the Early Holocene (~10-8 cal kyr BP) indicates a higher relative proportion of SSW that could be associate with higher production of the SSW, as has been recently observed in the South Atlantic, and/or with a possible reduction of the NPIW. Our data suggest that the present modern circulation pattern in the western subtropical Pacific Ocean was fully established after 4.6 cal kyr BP.

O Quadrilátero Ferrífero (MG) é uma importante unidade geotectônica do Cráton do São Francisco que alberga jazidas de ferro e ouro hospedadas na seqüência greenstone belt Rio das Velhas e cuja evolução geodinâmica esteve regida por vários eventos tectonometamórficos. Depósitos de ouro gerados por fluidos epitermais e remobilizações orogênicas proterozóicas se associam intimamente com camadas bandas de ferro e raramente disseminados em metapelitos no topo do greenstone. Nas mineralizações é comum uma paragênese que cristalizou mediante diversos processos e em distintos estágios com predomínio de sulfetos de ferro. Em geral os minérios possuem forte controle estrutural por dobras, falhas e cisalhamentos transcorrentes, desenvolvidos durante vários eventos deformacionais de diversa índole e estreita relação com processos de alteração hidrotermal como sericitização, carbonatação, cloritização, entre outros de menor incidência. O depósito de ouro Córrego do Sítio hospeda-se na seqüência silisiclástica de origem turbidítica metamorfisada em fácies xisto verde denominada Associação de Litofácies Ressedimentada que faz parte do Grupo Nova Lima, se apresenta disseminado em metapelitos e em veios de quartzo com carbonato. A mineralização que acompanha o ouro cristalizou em vários estágios principais nos que predominaram (i) pirita + pirrotita, (ii) arsenopirita + pirrotita + pirita com texturas finas e orientadas, (iii) arsenopirita com pirrotita e sulfosais em veios de quartzo, (iv) pirita grossa pervasiva em todas as rochas hospedeiras. O estudo da composição isotópica Pb, Sr e Nd, permitiu identificar que as fontes dos fluidos mineralizantes foram as rochas hospedeiras, que na evolução policíclica da mineralização participaram eventos metamórficos e hidrotermais a 2.2, 2.0 Ga. e sobreimpostos a ~600 Ma. os quais induziram os processos de circulação hidrotermal na área de estudo. Mediante comparativa com outros depósitos da região, sugere-se que os metais formadores do minério depositaram-se em Córrego do Sítio à idade de 2.2 Ga. originados a partir da BIF tipo São Bento e remobilizados por fluidos através de falhas inversas. Análises geocronológicas U-Pb (SHRIMP) e K-Ar embora não decisivos em quanto à determinação da idade da mineralização, revelaram a idade de ~2.7 Ga. como o limite temporal para a deposição das rochas hospedeiras. No contexto geológico aplicado se estabelece a potencialidade para a prospecção aurífera que apresentam as rochas metapelíticas do topo do Greenstone Belt Rio das Velas associadas a camadas bandadas de ferro com ouro, e que os alvos mais relevantes seriam zonas com falhas inversas e cisalhamentos transcorrentes. / The Quadrilátero Ferrífero is an important geotectonic unit of the São Francisco Craton that host iron and gold deposits within the vulcanosedimentary rocks of the greenstone belt Rio das Velhas. The geodynamic evolution of this greenstone includes several tectonometamorphic events. Gold deposits were formed by epithermal fluids, remobilized during the Proterozoic orogenic processes, are associated whit the banded iron formations and are sporadically disseminate in metapelitic rocks within the top of the greenstone sequence. In the ores is common the crystallization of iron sulfide minerals during diverse stages. Gold deposits have an important structural control by folds, reverse faults and strike-slip shearing zones, and are commons several hydrothermal alteration processes like sericitization, chloritization and carbonate usually related to the deformation. The Córrego do Sítio gold deposit is hosted in turbiditic siliciclastic rocks that are metamorphosed in the greenschist facies. The gold is associated with the iron sulfide arsenopyrite and pyrite, which are disseminated in metapelitic rocks and quartz-carbonate veins. The mineralization includes vary stages of crystallization, (1) pyrite and pyrrotite (2) arsenopyrite, pyrrotite and fine pyrite, (3) arsenopyrite whit pyrrotite and sulphosalts in quartz vein, and (4) pervasive pyrite. An integrated Pb, Sr e Nd, isotopic study of the Córrego do Sítio deposit allowed to identify that sources of the mineralizing fluids was the host rocks, that in the policiclic evolution the gold mineralizaton had participation events of metamorphism and hidrothermalism to age 2.2, 2.0 and 0.6 Ga. respectively the wich induced the hydrothermal circulation processes in the study area. The isotopic character of this deposit and its comparison with similar ones, suggest that the gold and its metals associated it is deposited in Córrego do Sítio to age 2.2 Ga. and that metals were derived from the banded iron formations, and remobilized by hidrothermal fluids across reverse faults. Although U-Pb (SHRIMP) and K-Ar geochronologic data were not conclusive to constrain the age of the mineralization, they provide to age ~2.7 Ga. that a good limit for the sedimentation of the host rock. It is suggest that there is a potential for gold prospection within the metapellitic rocks associated with banded iron formation of the Greenstone Rio das Velhas, and that the more relevant targets include areas with inverse and strike-slip fault.

O Quadrilátero Ferrífero (MG) é uma importante unidade geotectônica do Cráton do São Francisco que alberga jazidas de ferro e ouro hospedadas na seqüência greenstone belt Rio das Velhas e cuja evolução geodinâmica esteve regida por vários eventos tectonometamórficos. Depósitos de ouro gerados por fluidos epitermais e remobilizações orogênicas proterozóicas se associam intimamente com camadas bandas de ferro e raramente disseminados em metapelitos no topo do greenstone. Nas mineralizações é comum uma paragênese que cristalizou mediante diversos processos e em distintos estágios com predomínio de sulfetos de ferro. Em geral os minérios possuem forte controle estrutural por dobras, falhas e cisalhamentos transcorrentes, desenvolvidos durante vários eventos deformacionais de diversa índole e estreita relação com processos de alteração hidrotermal como sericitização, carbonatação, cloritização, entre outros de menor incidência. O depósito de ouro Córrego do Sítio hospeda-se na seqüência silisiclástica de origem turbidítica metamorfisada em fácies xisto verde denominada Associação de Litofácies Ressedimentada que faz parte do Grupo Nova Lima, se apresenta disseminado em metapelitos e em veios de quartzo com carbonato. A mineralização que acompanha o ouro cristalizou em vários estágios principais nos que predominaram (i) pirita + pirrotita, (ii) arsenopirita + pirrotita + pirita com texturas finas e orientadas, (iii) arsenopirita com pirrotita e sulfosais em veios de quartzo, (iv) pirita grossa pervasiva em todas as rochas hospedeiras. O estudo da composição isotópica Pb, Sr e Nd, permitiu identificar que as fontes dos fluidos mineralizantes foram as rochas hospedeiras, que na evolução policíclica da mineralização participaram eventos metamórficos e hidrotermais a 2.2, 2.0 Ga. e sobreimpostos a ~600 Ma. os quais induziram os processos de circulação hidrotermal na área de estudo. Mediante comparativa com outros depósitos da região, sugere-se que os metais formadores do minério depositaram-se em Córrego do Sítio à idade de 2.2 Ga. originados a partir da BIF tipo São Bento e remobilizados por fluidos através de falhas inversas. Análises geocronológicas U-Pb (SHRIMP) e K-Ar embora não decisivos em quanto à determinação da idade da mineralização, revelaram a idade de ~2.7 Ga. como o limite temporal para a deposição das rochas hospedeiras. No contexto geológico aplicado se estabelece a potencialidade para a prospecção aurífera que apresentam as rochas metapelíticas do topo do Greenstone Belt Rio das Velas associadas a camadas bandadas de ferro com ouro, e que os alvos mais relevantes seriam zonas com falhas inversas e cisalhamentos transcorrentes. / The Quadrilátero Ferrífero is an important geotectonic unit of the São Francisco Craton that host iron and gold deposits within the vulcanosedimentary rocks of the greenstone belt Rio das Velhas. The geodynamic evolution of this greenstone includes several tectonometamorphic events. Gold deposits were formed by epithermal fluids, remobilized during the Proterozoic orogenic processes, are associated whit the banded iron formations and are sporadically disseminate in metapelitic rocks within the top of the greenstone sequence. In the ores is common the crystallization of iron sulfide minerals during diverse stages. Gold deposits have an important structural control by folds, reverse faults and strike-slip shearing zones, and are commons several hydrothermal alteration processes like sericitization, chloritization and carbonate usually related to the deformation. The Córrego do Sítio gold deposit is hosted in turbiditic siliciclastic rocks that are metamorphosed in the greenschist facies. The gold is associated with the iron sulfide arsenopyrite and pyrite, which are disseminated in metapelitic rocks and quartz-carbonate veins. The mineralization includes vary stages of crystallization, (1) pyrite and pyrrotite (2) arsenopyrite, pyrrotite and fine pyrite, (3) arsenopyrite whit pyrrotite and sulphosalts in quartz vein, and (4) pervasive pyrite. An integrated Pb, Sr e Nd, isotopic study of the Córrego do Sítio deposit allowed to identify that sources of the mineralizing fluids was the host rocks, that in the policiclic evolution the gold mineralizaton had participation events of metamorphism and hidrothermalism to age 2.2, 2.0 and 0.6 Ga. respectively the wich induced the hydrothermal circulation processes in the study area. The isotopic character of this deposit and its comparison with similar ones, suggest that the gold and its metals associated it is deposited in Córrego do Sítio to age 2.2 Ga. and that metals were derived from the banded iron formations, and remobilized by hidrothermal fluids across reverse faults. Although U-Pb (SHRIMP) and K-Ar geochronologic data were not conclusive to constrain the age of the mineralization, they provide to age ~2.7 Ga. that a good limit for the sedimentation of the host rock. It is suggest that there is a potential for gold prospection within the metapellitic rocks associated with banded iron formation of the Greenstone Rio das Velhas, and that the more relevant targets include areas with inverse and strike-slip fault.